In the formation of contact openings or vias in semniconductor devices used to provide metal-to-metal or conductive layer-to-conductive layer contacts, it is often necessary to etch through one or more layers of insulative material formed over a substrate. FIG. 1 shows a cross section of a portion of a semiconductor device 10 in an intermediate stage of fabrication. The integrated circuit wafer section 10 has a substrate 12. The substrate is formed of a semiconductor material, for example silicon, or a semniconductor material over an insulator, for example silicon-on-insulator (SOI). Field oxide regions 13, transistor gate stacks 15, side wall spacers 17 protecting the gate stacks, and doped regions 19 are formed over the substrate. A layer of insulating material 21, which is usually a type of glass oxide available in the art, for example, Boro-Phospho-Silicate Glass (BPSG), or silicon oxide material such as silicon dioxide or Tetraethylorthosilicate (TEOS) is formed over the substrate 12. The layer of insulating material 21 may, in actuality, be formed as one or more layers of insulating material of, for example, BPSG, TEOS or silicon dioxide. The insulating layer 21 may be anywhere from a few hundred Angstroms to several thousand Angstroms in thickness. Formed over the insulative layer is a photoresist masking layer 23 using available photoresist materials. The photoresist layer 23 has a patterned opening 25 corresponding to the outline represented by the dotted lines shown in FIG. 1. The patterned opening forms the outline of a self-aligned contact (SAC) opening which is thereafter created. The SAC opening will provide access to the substrate 12 through the insulative layer 21.
Referring to FIG. 2, a plasma etch is then conducted to form the SAC opening 27, using the patterned opening 25 of the photoresist masking layer 23 as a guide. The patterned opening 25 generally follows the outline of the sides of the spacers 17 to align the etch for the contact opening. During the etching process, one or one fluorocarbons are introduced into a chamber containing the semiconductor device 10. Under suitable conditions ionic and neutral etchants are then formed to etch the insulative layer 21 so as to form the opening 27. Unfortunately, under prevailing conditions the reaction of these etchants and other species with the insulative material of layer 21 produces a polymer layer 29 on the bottom and side wall spacers of opening 27 as a reaction product. A thin accumulation of polymer layer 29 along the sides of the side wall spacers 17 may be desirable to prevent subsequent erosion of the spacers. However, a build up of polymer layer 29 at the bottom of the SAC opening 27 can cause an undesirable phenomenon known as “etch stop”, in which further etching through the insulative layer 21 to the surface of the substrate 12 is prevented by this polymer layer build up 29. In effect, the etch stop polymer layer 29 formed from the insulative layer can significantly inhibit suitable formation of the contact opening 27.
Attempts have been made to prevent etch stop during contact opening formation. For example, it is known to add oxygen (O2) to the mixture of fluorocarbon gases which are introduced into the reaction chamber. As a result, the etch rate of insulative material, e.g. oxide, has been shown to increase. The addition of oxygen appears to be accompanied by an increase in the density of the fluorine atoms in the etchant discharge. However, the use of too much oxygen may undesirably dilute the fluorine concentration, and thereby decrease the etch rate. Oxygen may also be utilized to clean polymer debris from the bottom of the contact opening after exposure to the fluorine-based etchant plasma. Nitrogen (N2) has also been utilized for cleaning residual debris after the etching process.
What is now needed in the art is a new method of forming a self-aligned contact opening in a semiconductor structure which can substantially eliminate etch stop problems. Also needed is a new composition which can be utilized in conjunction therewith.